The present invention relates to mechanisms of the type employing a rotatable shaft for performing an adjustment or change of operating characteristics for control of an appliance and particularly to mechanisms of the type wherein the appliance user positions a rotary knob attached to the shaft. Control adjustment mechanisms of this type are typically employed for appliances such as thermostats for controlling refrigerators, wall mounted thermostats for room heating and cooling control, and controls employed on household cooking and laundry appliances.
In cooking appliances and particularly appliances utilizing fuel gas burners, it has been found desirable to employ a push-to-turn shaft mounted rotary knob for controlling the burner ignition system. This type of push-to-turn knob control is particularly suitable for fuel burner ignition systems where it is desired to energize an automatic igniter commensurate with the opening of a fuel gas valve. In such gas burner controls, it is well known to provide a rotary cam attached to the knob shaft for setting the position of a switching mechanism which controls on electrically operated igniter. Push-to-turn controls of the latter type usually have a first rotary position for energizing the electrical igniter and a second rotary position for providing opening of the gas valve, e.g. an "ON" position.
Where fuel gas burners are employed in household appliances, it has been desired to provide a safety device on the burner control to prevent inadvertent user rotation of the control knob to an undesired position or tampering with the knob position by small children in a manner which would create a hazardous condition.
Heretofore, push-to-turn rotary shaft adjustment controls have employed a detent to fix the shaft in a desired safety or "OFF" Position when the shaft knob is rotated unless the shaft is pushed or the knob depressed, to cause the shaft detent to release, permitting rotation of the knob and the shaft. However, it has been found that with rapid rotation of the knob by the user, the knob may be inadvertently rotated past the detent position; and, this is particularly a problem where the detent employs a relatively weak spring. Thus it has long been desired to provide a way or means of providing a rotary adjustment mechanism for controlling an appliance which has a securely locked "OFF" position which prevents inadvertent rotation of the knob through the "OFF" position.